Patella injuries and complications from previous procedures are extremely difficult for the orthopedic surgeon to manage such procedures and have a limited success towards maintaining the patient's full function of the knee joint. Many different problems leave the surgeon with limited options. These problems can directly or indirectly result from trauma, chronic pain, or loss of bone due to a previous procedure, like a total knee replacement, where the patellar component loosened, became infected, or was painful. Often the complete patellar bone is removed or, in cases of a failed patellar resurfacing component, the bone loss are substantial and complications from subsequent procedures is relatively high. Loss of the patellar bone and the resulting loss of soft tissue balancing and tensioning compromises strength and articulation of the knee joint, and the patient's quality of life.
The prior art is cognizant of many different prosthetic devices for the replacement of the articulating surface of the patella commonly referred to as the knee cap. These devices have been designed for implantation in many cases where replacement of the articulating surface of the patella is indicated. There are many examples of such devices in the prior art and there are many devices which are commercially available to surgeons. One example of such a device can be had by reference to U.S. Pat. No. 5,019,104, entitled Patella Prosthesis and Method of Making the Same issued on May 28, 1991 to Leo A. Whiteside, et al. and assigned to Dow Coming Wright Corporation.
This patent discusses prior art devices in the background of the invention. Another patella replacement apparatus can be found in U.S. Pat. No. 4,007,495 entitled Patella Femoral Prosthesis which shows a device consisting of two components: a patella prosthesis and a femoral prosthesis, which are connected to each other. The femoral prosthesis is formed of steel and is attached by bone cement. The patella prosthesis is formed of polyethylene or a similar plastic material. The femoral prosthesis is mounted on the femur and the patella prosthesis is mounted on the patella. They are connected together by pressing the patella and the patella prosthesis towards the femoral prosthesis through a pin and slot arrangement.
U.S. Pat. No. 5,314,480 entitled Patella Components issued on May 24, 1994 and shows a patella replacement using a femoral component and a tibial component including a metal disk imbedded within a high molecular polyethylene disk. The polyethylene disk surrounds the edge of the metal disk so that the metal disk is flush with the polyethylene disk on one surface. The metal disk is provided with serrations which fit into the polyethylene disk to prevent rotation.
Patellar devices of various types and configurations have been utilized over the years to address the revision prosthetic patient and the complete patellectomy patient. For the patellectomy patient, the device must be able to fix biologically to remnant bone or soft tissue such as muscle or tendons. Additionally, the device must articulate and function within the confines of the cartilage on the femoral bone. The survivorship rate of devices that attempted to replace the patella has been poor and surgeons typically choose to remove the total patellar bone, leaving the patient with a compromised knee joint. Removal of the patellar bone creates about a 20% loss of the quadriceps mechanism muscle strength. Research has concluded that many patients only regain about 75% of their knee normal strength. For the case of removal of a failed prosthetic patellar component from a total knee joint replacement procedure, the amount of cancellous bone remaining is minimal and offers the surgeon a challenge for the new implant stability and long term fixation, while attempting to provide biomechancial articulation against the existing femoral component. The incidence of pain, lack of full function, and rate of component loosening is unacceptably high.
It is therefore an object of the present invention to provide an improved patella replacement device. The improved device as will be explained, can restore or mimic the biomedical function of the normal patella bone in severe cases. In this manner, the replacement by the patella replacement device of this invention results in an improved operation and improved muscle use for the patient. The device is simple to install as compared to prior art devices and offers advantages both to the surgeon and to the patient.